Energy harvester systems capture energy from varied sources, such as wind, movement of a person's arms, temperature differentials, pressure, or vibration. Since the power source may not be continuous, a battery may be used for storing energy, such as during calm periods of the wind. Batteries may need to be discharged continuously, even when being charged by the energy source. Thus simultaneous charging and discharging battery chargers are desirable in this and other applications.
Serial battery charging of two or more batteries may increase charging speed. Charging current may be balanced among several batteries in series. Reverse current between parallel batteries is avoided with serial charging.
However, serial charging may require a bypass path around an over-charged battery, or around a battery slot that has no battery installed. Sometimes the charging circuits are re-arranged when discharging occurs. Muxes or switches may be added to allow for circuit re-arrangement. Such circuit re-arrangement between charging and discharging operations is undesirable since simultaneous charging and discharging is not supported.
Blocking diodes are sometimes inserted in series with a battery. However, a series diode is undesirable since it may have a voltage drop, reducing the voltage and power applied to the battery. The diode voltage drop can seriously diminish efficiency.
What is desired is a serial battery charger that can simultaneously charge and discharge multiple batteries. A serial battery charger that protects individual batteries from over-charging is desirable. A serial battery charger that can bypass empty battery slot(s) in serial charging is desired. A serial battery charger that can output power from all batteries without circuit re-arrangement after charging is desired. Elimination of a blocking diode in series with a battery is also desirable. Balanced charging of multiple batteries without multiple charging units is also desired.